Investigation of the putative associations between dairy consumption and incidence of type 1 and type 2 diabetes.

A growing body of evidence suggests a possible relationship between the consumption of dairy products and the incidence of diabetes. A positive correlation between the early introduction of dairy in infancy and the incidence of type 1 diabetes (T1D) in genetically predisposed infants has been suggested by studies on rodents and humans. However, the lines of evidence supporting this association, including epidemiological studies and the observation of antibodies to bovine serum albumin, ß-casein and bovine insulin in the serum of patients with T1D, are not without controversy. On the other hand, an inverse relationship between the consumption of dairy foods and the development of metabolic syndrome and/or type 2 diabetes (T2D) has been implied by epidemiological studies. Several dairy components, especially milk proteins, are believed to play a role in the beneficial effect of dairy consumption on glucose regulation by modulation of incretin hormones. Other dietary factors have also been associated with the incidence of T1D and T2D, indicating that dairy foods might be only one among many dietary agents possibly implicated in the development of diabetes. The present paper critically reviews the evidence and plausible mechanisms for the putative associations between dairy food consumption and incidence of T1D and T2D.

Peptide array on cellulose support--a screening tool to identify peptides with dipeptidyl-peptidase IV inhibitory activity within the sequence of α-lactalbumin.

The inhibition of the enzyme dipeptidyl-peptidase IV (DPP-IV) is an effective pharmacotherapeutic approach for the management of type 2 diabetes. Recent findings have suggested that dietary proteins, including bovine α-lactalbumin, could be precursors of peptides able to inhibit DPP-IV. However, information on the location of active peptide sequences within the proteins is far from being comprehensive. Moreover, the traditional approach to identify bioactive peptides from foods can be tedious and long. Therefore, the objective of this study was to use peptide arrays to screen α-lactalbumin-derived peptides for their interaction with DPP-IV. Deca-peptides spanning the entire α-lactalbumin sequence, with a frame shift of 1 amino acid between successive sequences, were synthesized on cellulose membranes using "SPOT" technology, and their binding to and inhibition of DPP-IV was studied. Among the 114 α-lactalbumin-derived decamers investigated, the peptides 60WCKDDQNPHS69 (αK(i) = 76 µM), 105LAHKALCSEK114 (K(i) = 217 µM) and 110LCSEKLDQWL119 (K(i) = 217 µM) were among the strongest DPP-IV inhibitors. While the SPOT- and traditionally-synthesized peptides showed consistent trends in DPP-IV inhibitory activity, the cellulose-bound peptides' binding behavior was not correlated to their ability to inhibit the enzyme. This research showed, for the first time, that peptide arrays are useful screening tools to identify DPP-IV inhibitory peptides from dietary proteins.

Bioinformatics of edible yellow mealworm (Tenebrio molitor) proteome reveal the cuticular proteins as promising precursors of dipeptidyl peptidase-IV inhibitors.

Bioinformatics was applied for strategic processing of yellow mealworm (Tenebrio molitor) proteins to produce dipeptidyl peptidase (DPP)-IV inhibiting peptides. In silico analysis of 384 mealworm proteins revealed structural proteins as better precursors of DPP-IV inhibiting peptides, compared with other protein types, after pepsin and papain hydrolysis. This was associated with the higher hydropathicity and amounts of residues associated with DPP-IV inhibition in the structural (cuticular) proteins. In silico, the peptides were mostly released with pepsin than papain. Cuticular (CP) and non-cuticular proteins (NC) were extracted from yellow mealworm and hydrolyzed with pepsin and papain in vitro to validate the virtual findings. CP hydrolysate with papain inhibited DPP-IV the most compared to CP hydrolysate with pepsin, whereas NC hydrolysates were mostly inactive. CP had higher hydrophobic-hydrophilic amino acid ratios and contents of the activity-associated residues than NC. The findings demonstrate the application of bioinformatics in processing proteins for bioactive peptide production. PRACTICAL APPLICATIONS: The discovery of bioactive peptides from food proteins is typically based on the classic approach involving working with a small number of protein-protease combinations in vitro. For the first time, this study reported the application of in silico tools in comprehensively studying hundreds of proteins from yellow mealworm (an edible insect) as sources of DPP-IV inhibitors, followed by in vitro processing and validation guided by the results obtained in silico. The advantage of this approach is that it allows for analysis of several protein-protease combinations (with multiple datasets of structural, functional, and bioactivity parameters) in a short time. This work is relevant in advancing research on emerging or alternative proteins as well as structure-informed food protein processing. The bioinformatics approach can be adapted for strategic processing of proteins in the food industry prior to making major resource investments.

Investigation into the bioavailability of milk protein-derived peptides with dipeptidyl-peptidase IV inhibitory activity using Caco-2 cell monolayers.

In recent years, peptides derived from a variety of dietary proteins have been reported to exhibit inhibitory activity against the dipeptidyl-peptidase IV (DPP-IV) enzyme, a target in the management of type 2 diabetes. While much attention has been given to the production and identification of peptides with DPP-IV inhibitory activity from food proteins, particularly dairy proteins, little is known on the bioavailability of these molecules. In this study, the stability and transport of five previously identified milk-derived peptides (LKPTPEGDL, LPYPY, IPIQY, IPI and WR) and a whey protein isolate (WPI) digest with DPP-IV-inhibitory activity were investigated using Caco-2 cell monolayers as a model system for human intestinal absorption. Even though a small percentage (ranging from 0.05% for LPYPY to 0.47% for WR) of the bioactive peptides added to the apical side was able to cross the monolayer intact, all five peptides investigated were susceptible to peptidase action during the transport study. Conversely, only minor changes to the WPI digest composition were observed. Determination of the DPP-IV inhibitory activity of the peptides and amino acids identified in the apical and basolateral solutions showed that most degradation products were less effective at inhibiting DPP-IV than the peptide they originated from. Findings from this research suggest that the susceptibility of food-derived DPP-IV inhibitory peptides to degradation by intestinal brush border membrane enzymes may alter their biological activity in vivo. Further research should be conducted to enhance the bioavailability of DPP-IV inhibitory peptides.

Comparison of the susceptibility of porcine and human dipeptidyl-peptidase IV to inhibition by protein-derived peptides.

The enzyme dipeptidyl-peptidase IV (DPP-IV) is recognized to be a promising target for the management of type 2 diabetes. Over the last decade, numerous synthetic molecules and more recently, peptides from dietary proteins, have been reported to be able to inhibit DPP-IV activity. Most studies that have investigated the in vitro effect of these inhibitors have used porcine or human DPP-IV. Although structurally alike, it is unclear whether these two species display similar inhibition patterns. Therefore, the objective of this study was to compare the effects of protein-derived peptides on the activity of porcine and recombinant human DPP-IV. The two species showed different inhibition susceptibility to 43 of the 62 peptide sequences investigated. While 37 protein-derived peptides were more effective at inhibiting the porcine DPP-IV, only six caused a stronger inhibition of the activity of the human enzyme. Although the peptides WR, IPIQY and WCKDDQNPHS were found to be among the most potent inhibitors of both species, the inhibitory effect was greater on the porcine enzyme than on human DPP-IV (αKi or Ki=11.5, 13.4, 13.3 µM and 31.4, 28.2, 75.0 µM for porcine and human DPP-IV, respectively). Investigation into the mode of action of the most effective inhibitory peptides revealed that both species were inhibited in a similar manner by short fragments (≤5 amino acid residues), but that some of the longer peptides acted differently on the enzymes. This study shows that porcine DPP-IV is generally inhibited with greater potency by protein-derived peptides than is the human enzyme.

Overview of food products and dietary constituents with antidiabetic properties and their putative mechanisms of action: a natural approach to complement pharmacotherapy in the management of diabetes.

Diabetes is one of the fastest growing chronic, noncommunicable diseases worldwide. Currently, 11 major classes of pharmacotherapy are available for the management of this metabolic disorder. However, the usage of these drugs is often associated with undesirable side effects, including weight gain and hypoglycemia. There is thus a need for new, safe and effective treatment strategies. Diet is known to play a major role in the prevention and management of diabetes. Numerous studies have reported the putative association of the consumption of specific food products, or their constituents, with the incidence of diabetes, and mounting evidence now suggests that some dietary factors can improve glycemic regulation. Foods and dietary constituents, similar to synthetic drugs, have been shown to modulate hormones, enzymes, and organ systems involved in carbohydrate metabolism. The present article reviews the major classes and modes of action of antidiabetic drugs, and examines the evidence on food products and dietary factors with antidiabetic properties as well as their plausible mechanisms of action. The findings suggest potential use of dietary constituents as a complementary approach to pharmacotherapy in the prevention and/or management of diabetes, but further research is necessary to identify the active components and evaluate their efficacy and safety.

Isolation and characterization of peptides with dipeptidyl peptidase-IV inhibitory activity from pepsin-treated bovine whey proteins.

Inhibition of the enzyme dipeptidyl peptidase (DPP)-IV is one of the strategies used for the treatment of type 2 diabetes. In the present study, pepsin-treated whey protein isolate (WPI) and α-lactalbumin displaying DPP-IV inhibitory activity were fractionated by successive chromatographic steps and the resulting active fractions analyzed for their constituent peptides by liquid chromatography-electrospray ionization-tandem mass spectrometry. Among the identified sequences, 24 peptides derived from α-lactalbumin and 11 from ß-lactoglobulin were synthesized and their effects on DPP-IV activity assessed. The most potent fragments, LKPTPEGDL and LKPTPEGDLEIL (IC50=45 and 57 µM, respectively), were found to inhibit DPP-IV in an un-competitive manner. Although several of the peptides tested showed some inhibitory activity, only two were as effective as the un-fractionated WPI hydrolysate and none were as potent as the un-fractionated α-lactalbumin hydrolysate. The peptides' structural features, including length and amino acid composition, were found to impact their inhibitory activity. This study provides new insights on the active components responsible for the DPP-IV inhibitory activity of pepsin-treated whey proteins.

Inhibition of dipeptidyl peptidase (DPP)-IV and α-glucosidase activities by pepsin-treated whey proteins.

Inhibitors of the enzymes dipeptidyl peptidase (DPP)-IV and α-glucosidase are two classes of pharmacotherapeutic agents used for the treatment of type 2 diabetes. In the present study, whey protein isolate (WPI), α-lactalbumin, ß-lactoglobulin, serum albumin, and lactoferrin hydrolysates obtained by peptic digestion were investigated for their potential to serve as natural sources of DPP-IV and α-glucosidase inhibitors. Although inhibition of DPP-IV activity was observed in all pepsin-treated whey proteins studied, the α-lactalbumin hydrolysate showed the greatest potency with an IC50 value of 0.036 mg/mL. Conversely, only WPI, ß-lactoglobulin, and α-lactalbumin hydrolysates displayed some inhibitory activity against α-glucosidase. This study suggests that peptides generated from whey proteins may have dual beneficial effects on glycemia regulation and could be used as functional food ingredients for the management of type 2 diabetes.